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PEP-II IR Upgrade

VIEWS: 3 PAGES: 25

  • pg 1
									                                                  IR Upgrade
                                                  M. Sullivan




    PEP-II Interaction Region
            Upgrade

                 M. Sullivan




                   for the


          Super-B Factory Workshop
                   Hawaii
             January 19-22, 2004

                                     Super-B Factory Workshop
1                                    January 19-22, 2004
                                                       IR Upgrade
                                                       M. Sullivan



              •Present design
              •Upgrade parameters
              •Why upgrade the IR
    Outline
              •1st IR Upgrade Attempt
              •Beta functions
              •Crossing angle
              •Present IR Upgrade Study
              •SR fans and power
              •SR backgrounds
              •Summary


                                          Super-B Factory Workshop
2                                         January 19-22, 2004
                                                                    IR Upgrade
                                                                    M. Sullivan

    Machine Parameters that are Important for the IR

                        PEP-II       KEKB
    LER energy          3.1          3.5          GeV
    HER energy          9.0          8.0          GeV
    LER current         1.96         1.51         A
    HER current         1.32         1.13         A
     y*                12.5         6.5          mm
    x*                 25           60           cm
    X emittance         50           20           nm-rad
    Estimated sy*       5            2.2          mm
    Bunch spacing       1.26         2.4          m
    Number of bunches   1317         1284
    Collision angle     head-on      11          mrads
    Beam pipe radius    2.5          1.5          cm
    Luminosity          7.21033     11.31033    cm-2 sec-1
                                                       Super-B Factory Workshop
3                                                      January 19-22, 2004
                 IR Upgrade
                 M. Sullivan




    Super-B Factory Workshop
4   January 19-22, 2004
                                                                          IR Upgrade
                                                                          M. Sullivan

    PEP-II Proposed Upgrade Plans

                        Now        Projected   Upgrade
    LER energy          3.1        3.1         3.1       GeV
    HER energy          9.0        9.0         9.0       GeV
    LER current         1.8        3.6         4.5       A
    HER current         1.0        1.8         2.0       A
    y*                 12.5       8.5         6         mm
    x *                28         28          28        cm
    X emittance         50         40          40        nm-rad
    Estimated sy*       4.9        3.6         2.7       mm
    Bunch spacing       1.89       1.26        1.26      m
    Number of bunches   1034       1500        1700
    Collision angle     head-on    head-on     head-on   mrads
    Beam pipe radius    2.5        2.5         2.5       cm
    Luminosity          6.61033   1.81034    3.31034 cm-2 sec-1




                                                             Super-B Factory Workshop
5                                                            January 19-22, 2004
                                                               IR Upgrade
                                                               M. Sullivan




     Why Upgrade (Initial motivations)

    Lower the vertical beta function to 6-7 mm


    Keep maximum betas low


    Lower the beam-beam effect from the parasitic
    crossings


    Possibly get enough separation to allow filling
    every RF bucket

                                                  Super-B Factory Workshop
6                                                 January 19-22, 2004
                                                           IR Upgrade
                                                           M. Sullivan




      Initial upgrade attempt

    Replace the last 20 cm of each B1 magnet with
    quadrupole field (50% stronger than QD1 field)

    Introduce a crossing angle to recover beam
    trajectories so we don’t have to redesign or
    move any magnets. We need a certain amount
    of separation at QF2.

    Relatively easy change to make

    Moves the focusing closer to the IP


                                              Super-B Factory Workshop
7                                             January 19-22, 2004
                                            2x10 34 Interaction Region                                             IR Upgrade
                                                                                                                   M. Sullivan

                                            with a ±3.25 mrad Xangle
              30
                                                                             QF2                eV
                                                                                            G
                                                                                        1
                   QF5                QD4                                            3.
              20                                  Extra
                                                  focusing
                                                      QD1              QD1


              10
Centimeters




                   9 GeV


              0
                                                                                                     9 GeV


        -10
                                                      QD1              QD1
                                                   Extra
                                                   focusing
        -20                                                                        QD4               QF5
                                      eV
                                  G
                              1
                           3.               QF2

        -30
         -7.5               -5              -2.5                0            2.5         5                 7.5
                                                                                                      Super-B Factory Workshop
  8
                                                              Meters                                   M. Sullivan
                                                                                                      January 19-22, 2004
                                                                                                       Jun. 14, 2000
                                                                 IR Upgrade
                                                                 M. Sullivan


    Beta functions
       Low-energy beam
                    Present design
       beta x* (cm) beta y*(mm) beta x max   beta y max
       50           15            94         112
       35           12.5          135        135
       50           6             75         277
                    With Initial Attempt
       50           6             106        213

       High-energy beam
                    Present design
       50           15            520        450
       35           12.5          735        540
       50           6             528        1085
                    With Initial Attempt
       50           6             546        1057
                                                    Super-B Factory Workshop
9                                                   January 19-22, 2004
                                                                              IR Upgrade
                                                                              M. Sullivan




     Crossing angle and parasitic crossings
      Crossing angle
         Early last year, Ohmi-san from KEK announced that his beam-
         beam simulation code indicated a rapid luminosity degradation
         as a function of increasing crossing angle. Last summer, Yunhai
         Cai at SLAC confirmed Ohmi’s beam-beam result. The effect is
         most pronounced for very high tune shifts (~0.1).



      Parasitic crossings

         The introduction of a crossing angle increases the beam
         separation at the parasitic crossings which would lower the
         effect we presently see from parasitic crossings in by2
         bunch patterns. Lowering y* also increases parasitic
         crossing effects since the y at the PC is larger.
                                                                 Super-B Factory Workshop
10                                                               January 19-22, 2004
                            IR Upgrade
                            M. Sullivan




     Plot of
     luminosity
     degradation as a
     function of
     increasing
     crossing angle
     (courtesy of Yunhai Cai)




               Super-B Factory Workshop
11             January 19-22, 2004
                            LER First PC  , s = 9 mm                                                              LER First PC  , s = 7 mm                                                                    IR Upgrade
                                               y   l                                                                                     y       l
                  0.6                                                                          0.6                                                                                                              M. Sullivan
      PC     IP                                                                    PC     IP
     2 /                                                                        2 /
                  0.5                                          by*=0.9 cm                                                                                        by*=0.9 cm
                                                               by*=0.8 cm                      0.5
                                                                                                                                                                 by*=0.8 cm
                                                               by*=0.7 cm                                                                                        by*=0.7 cm
                                                               by*=0.6 cm
                                                                                                                                                                 by*=0.6 cm
                                                               by*=0.5 cm
                  0.4                                                                                                                                            by*=0.5 cm
                                                                                               0.4


                  0.3
                                                                                               0.3
                                                                                                                                                                                         The tune shift
                  0.2
                                                                                               0.2
                                                                                                                                                                                         from the first
                  0.1
                                                                                                                                                                                         parasitic crossing
                                                                                               0.1


                   0
                                                                                                                                                                                         normalized to the
                        0   2     4       6            8        10          12                  0
                                      /2 (mrad)
                                                                                                     0             2       4         6
                                                                                                                               /2 (mrad)
                                                                                                                                                     8            10          12
                                                                                                                                                                                         main collision
                                                                                                                                                                                         tune shift as a
                   LER PC tune shifts vs /2 for different y* normalized to
                     the IP tune shift for sl (bunch length) = 9 and 7 mm                                                                                                                function of
                                                                                                                                                                                         crossing angle
                            HER First PC  , s = 9 mm
                                                                                                                       HER First PC  , s = 7 mm
       PC
     2 /
             IP
                  0.6
                                               y       l
                                                                                                         0.6
                                                                                                                                                 y       l
                                                                                                                                                                                         and plotted for
                                                                                                                                                                                         various y*
                                                                                          PC    IP
                                                                                        2 /
                  0.5                                           by*=0.9 cm
                                                                by*=0.8 cm                               0.5                                                           by*=0.9 cm
                                                                by*=0.7 cm                                                                                             by*=0.8 cm
                                                                by*=0.6 cm                                                                                             by*=0.7 cm

                  0.4
                                                                by*=0.5 cm
                                                                                                         0.4
                                                                                                                                                                       by*=0.6 cm
                                                                                                                                                                       by*=0.5 cm
                                                                                                                                                                                         values for PEP-II
                  0.3
                                                                                                         0.3
                                                                                                                                                                                         (courtesy of Marica
                  0.2
                                                                                                                                                                                         Biagini)
                                                                                                         0.2


                  0.1
                                                                                                         0.1


                    0
                                                                                                          0
                        0   2     4        6               8     10          12
                                                                                                               0       2        4            6               8          10          12
                                      /2 (mrad)                                                                                    /2 (mrad)

                        HER PC tune shifts vs /2 for different y* normalized to
                                                                                                                                                                                                   Super-B Factory Workshop
12                              the IP tune shift for sl = 9 and 7 mm                                                                                                                              January 19-22, 2004
                                                                IR Upgrade
                                                                M. Sullivan


       Present Working Design Constraints
     Keep head-on collisions


     Increase the beam separation at the 1st parasitic
        collision as much as possible


     Allow for 6-7 mm y*


     Do not change QF2 septum magnet




                                                   Super-B Factory Workshop
13                                                 January 19-22, 2004
                                                                                   IR Upgrade
                                                                                   M. Sullivan

         Present Working Design
     Stronger B1 magnet to increase separation at 1st
       parasitic crossing
           20% stronger first 5 slices (first 12.5 cm with the weakest
           field and the largest lever arm)

     Slightly increase the beam energy asymmetry
           9.1 x 3.08 GeV

     Stronger, closer QD1 magnets
           30% stronger slices for 1st 5 slices
           Move radial ion pump behind B1 to behind QD1
           Put higher strength focusing in present pump place
           Minimal hardware change


           Higher strength material has higher temperature
           coefficient                                     Super-B Factory Workshop
14                                                                   January 19-22, 2004
                                            IR Upgrade
                                            M. Sullivan

     Modified Head-on design




                               Super-B Factory Workshop
15                             January 19-22, 2004
                                                                               IR Upgrade
                                                                               M. Sullivan
     Orbit comparison with upgrade and present design
                                                                   Work in
                                                                   progress
                                       1st horizontal corrector




                                                                  +z side

                   1st vertical corrector                         LER beam




                                                                  Super-B Factory Workshop
16                                                                January 19-22, 2004
                                                                 IR Upgrade
                                                                 M. Sullivan



                                                     Work in
                                                     progress
                         1st horizontal corrector




                                                    +z side

     1st vertical corrector                         HER beam




                                                    Super-B Factory Workshop
17                                                  January 19-22, 2004
                                                                          IR Upgrade
                                                                          M. Sullivan

             Steps toward a new design
     Need to correct the position and angle in the x and y
     orbit on the +Z and –Z sides for each beam (8 orbits in
     total – two constraints for each orbit)

     Too many variables for 8 total correctors

     Allow adjusting the vertical collision point

     Allow adjusting the horizontal collision angle

     Allow the new sections of QD1 to have a variable
     offset (variable bending – but it affects both beams)

     Allow (small) beam energy adjustments as long as we
     are still on the 4S resonance
                                                             Super-B Factory Workshop
18                                                           January 19-22, 2004
                                                                                IR Upgrade
                                                                                M. Sullivan

     Beta functions (revisited)
         Low-energy beam
                            Present design
         x* (cm)           y* (mm)          x max (m)   y max (m)
         50                 15                94           112
         35                 12.5              135          135
         50                 6                 75           277
                            With upgrade #1
         50                 6                 106          213
                            With upgrade #2
         50                 6                 99           213
         35                 6                 134          213

         High-energy beam
                            Present design
         50                 15                520          450
         35                 12.5              735          540
         50                 6                 528          1085
                            With upgrade #1
         50                 6                 546          1057
                            With upgrade #2
         50                 5                 570          970
         35                 5                 795          970
                                                                   Super-B Factory Workshop
19                                                                 January 19-22, 2004
                                                                       IR Upgrade
                                                                       M. Sullivan

     SR fans and power
      The proposed high beam currents (4.5A LER and 2A
      HER) will generate a large amount of SR in the IR

      The HER vacuum elements were designed for 2A so
      the HER parts should be OK. There is some question
      about the High-Power Downstream Dump that
      absorbs the HER B1 SR power

      There are 2 vacuum chambers that see the LER SR
      power that need to be looked at more closely
         The LER downstream crotch chamber that sees B1 radiation

         The upstream LER SR mask for the Be beam pipe. It sees
         upstream QD1 radiation


                                                          Super-B Factory Workshop
20                                                        January 19-22, 2004
                  IR Upgrade
                  M. Sullivan




     Super-B Factory Workshop
21   January 19-22, 2004
                  IR Upgrade
                  M. Sullivan




     Super-B Factory Workshop
22   January 19-22, 2004
                                                                    IR Upgrade
                                                                    M. Sullivan


     SR fans and power (cont.)
     The present power levels on the multi-tipped
     LER SR mask are about 30 W/mm at 2.1A beam
     current. This goes to 50 W/mm at 3.6A and 65
     W/mm for 4.5 A of LER beam. This mask is under
     study. Presently it looks like this chamber may
     just work at 3.6 A but that it will need to be rebuilt
     for a 4.5 A beam

     The crotch chamber design allowed for
     overlapping B1 radiation fans. This can only
     happen when the detector solenoid is off. We
     never intend to run high current beams with the
     solenoid off so we have some margin here.

                                                       Super-B Factory Workshop
23                                                     January 19-22, 2004
                                                                     IR Upgrade
                                                                     M. Sullivan




     SR backgrounds
      The present LER SR mask (multi-tipped mask) does?
      (not completely checked yet) an adequate job of shielding
      the detector if we upgrade the B1 and QD1 magnets. We
      are trying to maintain the beam orbits such that the
      present design will work with minor modifications.


      In any case, the extra power from the higher current
      LER beam means that SR backgrounds have to be
      studied in more detail


      The very high beam current of the LER means that we
      need to check to make sure that back-scattered photons
      from the downstream crotch chamber do not strike the
      detector beam pipe

                                                        Super-B Factory Workshop
24                                                      January 19-22, 2004
                                                                                  IR Upgrade
                                                                                  M. Sullivan

                   Summary
     The initial upgrade proposal replaced the last 4 slices of the B1
     magnets with quadrupole field. This allows for lower beta y* values
     with a smaller increase in the maximum beta y.
     The replacement of the B1 slices with quad field introduces a ± 3.3
     mrad crossing angle at the IP which reduces the beam-beam effect at
     the 1st parasitic crossing. However, recent beam-beam simulations
     indicate a luminosity reduction for beams with a crossing angle.
     An alternative proposal currently under study is to strengthen the IP
     end of QD1 effectively moving the center of the magnet closer to the
     IP. At the same time, increase the beam separation at the 1st parasitic
     crossing by increasing the strength of the initial B1 slices. This
     maintains the PEP-II head-on collision.
     The high beam currents of the upgrade plans generate significant
     SR power in the IR that must be handled
     SR backgrounds look like they can be controlled but have not yet
     been thoroughly studied

                                                                     Super-B Factory Workshop
25                                                                   January 19-22, 2004

								
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